1. Field
The present embodiments relate to a magnetic detection device having magnetic-resistance elements, and more particularly, to a magnetic detection device of a NS detection type capable of simplifying a circuit configuration with a decrease in the number of elements.
2. Related Art
FIG. 17 is a circuit diagram of a known magnetic detection device. The magnetic detection device includes a sensor unit S and an integrated circuit (IC) 1. The magnetic detection device shown in FIG. 17 is a NS detection type sensor. The NS detection type sensor detects both the positive magnetic field and negative magnetic field, for example north pole direction and south pole direction. The sensor unit S has a first bridge circuit BC1 including first magneto-resistance elements 2 such as a GMR element of which electric resistance varies with an external magnetic field in a positive direction and a second bridge circuit BC2 including second magneto-resistance elements 3, such as a GMR element, that has a variable resistance in response to an external magnetic field in a negative direction. “An external magnetic field in a positive direction” generally indicates the external magnetic field in any random direction, but in FIG. 17, that indicates the external magnetic field in the direction in which the resistance of the first magneto-resistance elements 2 varies but the resistance of the second magneto-resistance elements 3 does not vary (i.e. functions as a fixed resistance element). “An external magnetic field in a negative direction” indicates an opposite direction of the external magnetic field in the positive direction, and in FIG. 17, that indicates the direction of the external magnetic field in which the resistance of the second magneto-resistance elements 3 is not fixed but the resistance of the first magneto-resistance elements 2 is fixed (i.e. function as fixed resistance element).
As shown in FIG. 17, the first magneto-resistance elements 2 and the fixed resistance elements 4 form series circuits respectively, and the series circuits are connected in parallel to each other to form the first bridge circuit BC1. Each output extracting portion of two series circuits forming the first bridge circuit BC1 is connected to a first differential amplifier 6. As shown in FIG. 17, each second magneto-resistance element 3 and each fixed resistance element 5 forms a series circuit, and the series circuits are connected in parallel to each other to form the second bridge circuit BC2. Each output extracting portion of two series circuits forming the second bridge circuit BC2 is connected to a second differential amplifier 7.
Inside the integrated circuit 1 is provided with not only the differential amplifiers 6 and 7, but also schmitt trigger type comparators 12 and 13, latch circuits 8 and 9, and the like. An external magnetic field detection signal is taken out from external output terminals 10 and 11.
If the external magnetic field in the positive direction acts on the magnetic detection device shown in FIG. 17, then the resistance of the first magneto-resistance elements 2 forming the first bridge circuit BC1 is varied. As the result, an output of the first bridge circuit BC1 is amplified in the first differential amplifier 6, and the detection signal caused by the amplified output is generated, then the detection signal is outputted from the first external output terminal 10. On the other hand, if the external magnetic field in the negative direction acts on the magnetic detection device, then the resistance of the second magneto-resistance elements 3 forming the first bridge circuit BC2 is varied. As the result, an output of the second bridge circuit BC2 is amplified in the second differential amplifier 7, and the detection signal caused by the amplified output is generated, then the detection signal is outputted from the second external output terminal 11.
As mentioned above, the magnetic detection device shown in FIG. 17 includes a NS detection type sensor which is detectable in any direction (such as the positive and negative directions) of the external magnetic field.
The following references are examples of the related art: JP-A-2004-77374, JP-A-2004-180286, JP-A-2005-214900, JP-A-2003-14833, JP-A-2003-14834, JP-A-2003-121268 and JP-A-2004-304052.
However, the magnetic detection device in the past shown in FIG. 17 needs a lot of elements for putting together the sensor unit S. Specifically, to configure the NS detection type sensor, two bridge circuit, BC1 and BC2, is respectively needed, consequently, totally eight number of elements are needed.
Since the magnetic detection device includes two bridge circuits BC1 and BC2, the differential amplifiers 6 and 7, the comparators 12 and 13, signal lines and the like need to be provided in each bridge circuit BC1 and BC2, so the circuit configuration is complicated, and also there is an obstacle to decrease in size of the integrated circuit 1.